1. Field of the Invention
This invention relates to graft copolymers containing cationic groups in the polymer chain.
2. Description of the Related Art
It is well known to blend low Tg (glass transition) elastomers with more brittle thermoplastic polymers having a higher Tg to yield blends with improved toughness and impact strength. The desired properties are only obtained by achieving a fine dispersion of the elastomer in the thermoplastic polymer.
It is also well known to form blends of relatively highly unsaturated elastomers such as polybutadiene or natural rubber with elastomers having less or no ethylenic unsaturation, e.g., butyl rubber, halogenated butyl rubber, copolymers of isobutylene and a para-alkylstyrene, ethylene/propylene or ethylene/propylene/diene rubber and the like, in order to enhance the properties of vulcanizates based on such blends. Such property enhancement includes improved oil and grease resistance, improved resistance to oxygen and ozone degradation, improved abrasion resistance and improved impermeability to air, water vapor and many organic solvents.
One of the major problems associated with the formation of such blends is that most of these polymer components are mutually incompatible. Poor mutual adhesion at the blend phase boundaries in such systems results in a diminishment of physical properties of the polymer blend.
It is well established that the use of appropriately structured polymer compatibilizers as additives in such systems can markedly enhance physical properties. These additives are typically block or graft copolymers in which polymer segments interact in a favorable manner with each polymer phase of the blend. This "bridging" at the interfacial blend region enhances the interfacial adhesion, and improves the dispersion and size of the discrete blend phase and improves mechanical properties. Thus, for example, a block or graft copolymer containing both polybutadiene and polystyrene polymer units can serve as a compatibilizer in a polymer system comprising a blend of polystyrene and polybutadiene.
Analogs of halogenated butyl rubber have been recently discovered which comprise the halogenated product of a random copolymer of a C.sub.4 to C.sub.7 isomonoolefin, e.g. isobutylene, and a para-alkystyrene, e.g. paramethylstyrene, such as disclosed in U.S. Pat. No. 5,162,445. Although these materials are devoid of olefinic backbone unsaturation, the presence of a benzylic halogen, e.g. bromine, permits facile crosslinking or curing of the polymers using, for example, zinc oxide/stearic acid curing systems. In addition, functionalized versions of these copolymers may be prepared by nucleophilic substitution of the benzylic halogen present in the polymer molecules with a reagent reactive therewith to provide polymers containing amine, acid, ester, amide, onium and the like functionality. Grafted polymers may also be prepared by a graft-onto reaction wherein the halogenated copolymer is reacted in solution with a polymeric nucleophile such as polystyryl lithium. These graft-onto reactions lead to the production of solvent soluble grafted copolymers which are disclosed to be useful as compatibilizers for polymer blends, e.g., blends of polyisobutylene, butyl rubber or halogenated copolymers of isobutylene and paramethylstyrene with polystyrene.